1. Field of the Invention
The present invention concerns fibrous reinforcements that are suitable for use as fireproofing agents. The invention is especially applicable in the area of composite items used in the automobile, aeronautical or naval industries.
2. Description of Related Art
Composite items are typically composed of a fibrous component and a resin or matrix component. Such composite items may be fabricated using a process called “direct” or a process called “indirect.” A direct process is defined by the fact that one or more fibrous reinforcements are used in the “dry” state. In the dry state, fibrous reinforcements do not include the final matrix. The resin or matrix, which is thermoplastic, thermosetting, or a combination of the two types, is brought in separately. For example, the resin may be brought in by injecting it into a mold containing the reinforcing fibers. This process is known as the resin transfer molding (RTM) process. Another process for bringing in the resin involves infusion into a mold and throughout the thickness of the fibrous reinforcements. This process is known as the liquid resin infusion (LRI) process or the resin film infusion (RFI) process. Other processes include manual coating/impregnation with a roller or brush on each of the single layers of the fibrous reinforcement which are applied successively on the form. An indirect process is defined by the fact that the fibers and the resin are first associated before they are used.
For the RTM, LRI or RFI processes, generally a fibrous preform in the shape of the desired finished article must first be fabricated then impregnated with a thermoplastic or thermosetting resin. The resin is injected or infused by suction and then thermoset to harden it after polymerization.
Composite items used in the automobile, aeronautical or naval industries especially are subject to very strict requirements as to non-flammability. There are different ways to make a composite material flame-resistant. The solutions are relatively well known to a person skilled in the art with regard to composite materials obtained by an indirect process.
In high-performance applications of composite materials, fibrous materials impregnated with a resin, usually called “preimpregnates” or “prepregs,” are the most used intermediate materials. For example, U.S. Pat. No. 5,714,419 describes a prepreg comprising a modified thermosetting resin containing a flame retardant, and a substrate of carbon paper impregnated with the resin, the substrate containing carbon fibers in polyacrylonitrile and an alcohol binder. The flame retardant may be a halogenated compound, an antimony compound, or an organic phosphate.
In the case of prepregs, the resin that is impregnated in the fibrous reinforcement may later be modified by fireproofing agents of all types, especially those that would not be solubilized or that would significantly increase the viscosity of the resin.
For resins to be used in direct processes (RTM, RFI, LRI and the like.), it is not possible to use solid modifiers dispersed in said resin because the modifiers would be retained (filtered) by the fibrous reinforcement and the result would be a composite material that is not homogeneous in composition. It is also not possible to use modifiers that might increase the viscosity of the injected or infused resin without too great and too negative a modification of the fabrication process parameters. Thus, these imperatives must be taken into account when formulating resins for direct processes. This usually leads to modified resins that have defects of performance, defects of use or defects of composition in the light of regulations that do not authorize halogenated fireproofing agents, for example. That is why it has sometimes been proposed to modify the composite material with a later treatment.
For example, U.S. Pat. No. 5,389,435 proposes a composite material based on carbon fibers and epoxy resin on the surface of which is laid a fiberglass canvas coated with a compound that includes a silicate-type inorganic load and an epoxy resin that may be identical to the resin in the composite material. Such a solution is costly because the ultimate property of fire resistance is not obtained directly. Furthermore it is not satisfactory because the item is made heavier by layering while there is no gain in mechanical performance.
It must also be emphasized that to obtain the materials described in the two patents mentioned above, it is necessary to use methyl ethyl ketone-type solvents that are toxic to health and the environment.